Glacial retreat sedimentation in the Smalfjord Formation, Late Precambrian, North Norway

Tillites, conglomerates and sandstones occurring in the basal part of the Smalfjord Formation along the Varangerfjord, East Finnmark, North Norway are believed to have formed during the retreat of a glacier. At Kvalnes, on the south side of the fjord, the following sequence, up to 20 m thick, is found: (1) massive monomict tillite interpreted as a subglacial till, (2) massive polymict tillite with lenticular intercalations of stratified sandstone and tillite, interpreted as supraglacial/proglacial drift, (3) polymict conglomerate interstratified with laminated sandstones, interpreted as braided stream deposits. The last named interfingers laterally and is overlain by marine sandstones. At Bigganjargga, near the head of the fjord, a lens of tillite about 3 m thick rests on a striated pavement and is overlain by sandstones and shales. Part of the tillite, containing irregular patches of slightly winnowed tillite, is interpreted as a melt-out till, while a marginal part consisting of inclined tillite beds is interpreted as a series of flow till deposits. The lens is believed to be an oblique section through what was originally an ice-cored moraine ridge. During a subsequent transgression, the moraine was partially eroded, a lag conglomerate was formed, and overlying marine sediments were deposited. Bedded flow tills formed in a supraglacial/proglacial environment may be preserved where the extent of current reworking is very low (such as an isolated end moraine). Stratified conglomerate and sandstone, intimately intercalated with tillite, is to be expected at a glacier margin where glacial meltwater is locally and occasionally abundant, and glacier ablation permits downslope flowage of mobilized supraglacial fluid till.     

Shallow-water gravity-flow deposits, Chapel Island Formation, southeast Newfoundland, Canada

A remarkable suite of shallow-water, gravity-flow deposits are found within very thinly-bedded siltstones and storm-generated sandstones of member 2 of the Chapel Island Formation in southeast Newfoundland. Medium to thick siltstone beds, termed unifites, range from non-graded and structureless (Type 1) to slightly graded with poorly developed lamination (Type 2) to well graded with lamination similar to that described for fine-grained turbidites (Type 3). Unifite beds record deposition from a continuum of flow types from liquefied flows (Type 1) to turbidity currents (Type 3). Calculations of time for pore-fluid pressure dissipation support the feasibility of such transitions. Raft-bearing beds consist of siltstone with large blocks or‘rafts’ of thinly bedded strata derived from the underlying and adjacent substrate. Characteristics suggest deposition from debris flows of variable strength. Estimates of debris strength and depositional slope are calculated for a pebbly mudstone bed using measurable and assumed parameters. An assumed density of 2.0 g cm^-1 and a compaction estimate of 50% gives a strength estimate of 79.7 dyn cm^-2 and a depositional slope estimate of 0.77°. The lithologies and sedimentary structures in member 2 indicate an overall grain-size distribution susceptible to liquefaction. Inferred high sediment accumulation rates created underconsolidated sediments (metastable packing). Types of sediment failure included in situ liquefaction (‘disturbed bedding’), sliding and slumping. Raft-bearing debrites resulted from sliding and incorporation of water. Locally, hummocky cross-stratified sandstone directly overlies slide deposits and raft-bearing beds, linking sediment failure to the cyclical wave loading associated with large storms. The gravity flows of the Chapel Island Formation closely resemble those described from the surfaces of modern, mud-rich, marine deltas. Details of deltaic gravity-flow deposition from this and other outcrop studies further our understanding of modern deposits by adding a third dimension to studies primarily carried out with side-scan sonar.     

Analcime in lake and lake-margin sediments of the Carboniferous Rocky Brook Formation, Western Newfoundland, Canada

In the Deer Lake Basin of western Newfoundland, Canada, analcime has been found within fine-grained, siliciclastic and carbonate, lake and lake-margin sediments of the Carboniferous Rocky Brook Formation. Analcime is the only zeolite observed in these unmetamorphosed and non-volcanogenic rocks. Microscopic analcime occurs as vug-filling, limpid, isotropic to anisotropic crystals. Microprobe analyses show this type of analcime to be lower in silica than most analcime in sedimentary rocks. A second textural type of finer-grained submicroscopic analcime can be detected from X-ray diffraction spectra of Rocky Brook Formation mudstones, where it is associated with phyllosilicates (illite, interstratified chlorite/smectite, smectite, chlorite), other silicates (quartz, feldspar) and carbonates (dolomite, calcite). Results of this study suggest that the analcime in the Rocky Brook Formation formed either by direct lakewater/porewater precipitation or by reaction of these waters with one or more clay mineral types or plagioclase.     

Precambrian sedimentation,tectonics, and magmatism in Mexico

Present status of geologic mapping indicates that there are three major units of Precambrian rocks in Mexico. The oldest (older than 1,700 m. y.) and the youngest (younger than 700 m. y.) are confined to the northwest part of the country. The intermediate unit (1,300-800 m. y.) is distributed in eastern and southern Mexico and extend into northern Guatemala.The rocks making up the oldest unit accumulated as greywackees and associated volcanics in a eugeosyncline prior to 1,700 m. y. ago; this eugeosyncline extended into Mexico from the north-northeast, where it bordered the older Precambrian craton. These rocks underwent metamorphism and anatexis around 1,700 m. y. ago, that produced the development of the amphibolite-granulite facies and the emplacement of granitic stocks and batholiths.A similar history, but somewhat younger, is recorded for the Precambrian rocks in eastern and southern Mexico. These rocks accumulated in the southern continuation of the Grenville Geosyncline as greywackees and volcanics, starting about 1,300 m. y. ago. These rocks underwent metamorphism and anatexis during the interval of 1,000-900 m. y. ago to form the Oaxacan Structural Belt.An event of granitic magmatism, around 700 m. y. ago, is evidenced in the extreme northwest and southeast of Mexico which, heretofore is not recognized in Texas. In the northwest, this was followed by the intrusion of diabase dykes, prior to the deposition of the youngest Precambrian sediments.During latest Precambrian time, in northwest Mexico, an about 2,000 m thick sequence of conglomerate, sandy shale and dolomite, containingCollenia, Cryptozoa and other organisms, accumulated on top of the eroded older Precambrian metamorphics and granitic rocks, that formed the northeast flank of the miogeosynclinal part of the ancestral North American Cordilleran Geosyncline, representing a near-shore facies. These rocks deformed together with the overlying Paleozoic sedimentary rocks at the end of the Paleozoic, during the Sonoran Orogeny.The present abrupt truncation in the west of both the older and youngest Precambrian rocks in northwest Mexico against the Gulf of California, is the result of the combination of late Paleozoic movements along the Texas Lineament and Torreón-Monterrey Fracture Zone, of the regeneration due to Early Jurassic metamorphism and anatexis, and of movements along the late Mesozoic-Tertiary San Andreas Fault System. A similar truncation of the younger Precambrian rocks in southern Mexico against the Pacific Ocean crust, is considered to be result of a combined thrust and left-lateral movement along the Jalisco-Nicoya Fault during medial Tertiary time.

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Zusammenfassung Nach dem augenblicklichen Stand der geologischen Kartierung gibt es drei Haupteinheiten präkambrischer Gesteine in Mexiko. Die ältesten (> 1700 M. J.) und die jüngsten (< 700 M. J.) sind auf den Nordwestteil des Landes beschränkt, während die mittlere Einheit (1300-800 M. J.) in Ost- und Südmexiko vorkommt und sich bis nach Nord-Guatemala erstreckt.Die Gesteine der ältesten Serie - Grauwacken und vulkanische Gesteine — wurden vor mehr als 1700 M. J. in einer Eugeosynklinale abgelegt, die nach Mexiko von NNE her hineinreichte, wo sie einen noch älteren Kraton begrenzte. Vor etwa 1700 M. J. wurden diese Gesteine der Metamorphose und Anatexis unterzogen; daraus resultierte die Amphibolit-Granulit-Fazies, die Platznahme von Granitstöcken und Batholiten.Eine ähnliche Geschichte hatten die jüngeren präkambrischen Gesteine Ostund Süd-Mexikos. Hier wurden, beginnend etwa vor 1300 M. J., in der südlichen Fortsetzung der Grenville-Geosynklinale Grauwacken und vulkanische Gesteine abgelagert. Vor 1000-900 M. J. fanden Metamorphose und Anatexis statt, und der Oaxacan-Strukturbogen entstand.Granitischer Magmatismus fand vor etwa 700 M. J. im äußersten Nordwesten Mexikos (ebenfalls südöstlich von Mexiko) statt, der in Texas bisher nicht nachgewiesen wurde. Ihm folgten Diabasintrusionen; nach denen kam es zur Ablagerung jüngster präkambrischer Sedimente.Im jüngsten Präkambrium wurde in NW-Mexiko eine etwa 2000 m mächtige Serie von Konglomeraten, sandigem Tonstein und Dolomit (Collenia, Cryptozoa und andere Organismen enthaltend) abgelagert, und zwar diskordant auf älter präkambrischen metamorphen und granitischen Gesteinen. Sie bildeten in Küstenfazies die Nordostflanke des miogeosynklinalen Teiles der angestammten nordamerikanischen Kordilleren-Geosynklinale. Sie wurden zusammen mit den überlagernden paläozoischen Sedimenten am Ende des Paläozoikums gefaltet (Sonoran-Orogenese).Das heutige plötzliche Aufhören der älteren und der jüngsten präkambrischen Gesteine Nordwest-Mexikos im Westen gegen den Golf von Kalifornien ist das Ergebnis der Kombination von spätpaläozoischen Bewegungen entlang dem Texas-Lineament und der Torreón-Monterrey-Bruchzone (s. Abb. 11), ihrer Regeneration während frühjurassischer Metamorphose bzw. Anatexis und von Bewegung entlang der spätmesozoisch-tertiären San-Andreas-Bewegung. Ein ähnliches Aufhören der jüngeren präkambrischen Gesteine in Süd-Mexiko gegen die Kruste des Pazifiks gilt als das Ergebnis gleichzeitiger Überschiebung und linksseitlicher Seitenverschiebung im mittleren Tertiär entlang der Jalisco-Nicoya-Verwerfung.

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Resumen El estado actual de la cartografía geológica indica que existen tres unidades principales de rocas precámbricas en México. La unidad más antigua (más antigua que 1,700 m. a) y la más reciente (más reciente que 700 m. a.) se limitan para la parte noroccidental del país. La unidad intermedia (1,300-800 m. a.) se encuentra en las partes oriental y meridional de México, y se extiende a la parte septentrional de Guatemala.Las rocas, que constituyen la unidad más antigua, se acumularon como grauvacas y rocas volcánicas relacionadas en un eugeosinclinal, antes de 1,700 m. a.; este eugeosinclinal se extendió a México desde el norte-noreste, donde rodeó un cratón precámbrico aún más antiguo. Estas rocas sufrieron metamorfismo y anatexis cerca de 1,700 m. a., procesos que produjeron el desarrollo de la facies de anfibolita-granulita y el emplazamiento de troncos y batólitos graniticos.Una historia similar, aunque algo más reciente, registran las rocas precámbricas en las partes oriental y meridional de México. Estas rocas acumularon en la prolongación meridional del Geosinclinal Grenville, como grauvacas y rocas volcánicas, a partir, hace aproximadamente de 1,300 m. a. Estas rocas pasaron por metamorphismo y anatexis durante el período comprendido entre 1,000 y 900 m. a., para formar la Faja Tectónica Oaxaqueña.Un evento de magmatismo granítico, ocurrido hace cerca de 700 m. a., se manifiesta en los extremos noroccidental y suroriental de México, y el cual aún no se ha identificado en Texas. En el noroeste, este evento fue seguido por la intrusión de diques de diabasa, antes del depósito de los sedimentos precámbricos de los más recientes.Durante el Precámbrico lo más tardío, en el noroeste de México, se acumuló una sequencia de cerca de 2,000 m de espesor, encima de las rocas metamórficas y graníticas precámbricas más antiguas profundamente erosionadas que formaron en flanco nororiental de la parte miogeosinclinal del ancestral Geosinclinal Cordillerano de Norte América; la secuencia consiste en conglomerado, lutita arenosa, y dolomita conCollenia, Cryptozoa, y con otros organismos, representando una facies cercana a la costa.La terminación actual abrupta occidental de las rocas precámbricas más antiguas y las más recientes en el noroeste de México contra el Golfo de California, es el resultado de movimientos paleozoicos tardios a lo largo del Almeamiento de Texas y de la Zona de Fracturamiento Torreón-Monterrey, de la regeneración producida por el rnetamorfismo y anatexis durante el Jurásico Temprano, y de movimientos a lo largo del Sistema de Fallas San Andreas durante el Mesozoico tardío-Terciario. Un truncamiento similar de las rocas precámbricas más recientes en el sur de México contra la corteza del Océano Pacífico, se considera como resultado tanto de movimiento lateral sinistral como de cabalgamiento a lo largo de la Falla Jalisco-Nicoya, durante el Terciario medio.

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₁ : (_h700 ) ( 700 ) - ; (1300-800 ) . — — 1700 , NNE . 1700 , - , . . , 1300 Grenville . 1000-900 n. 700 - ( - ) , . , . NW – 2000 — , ( Collenia, Cryptozoa ). - . . - Terreon-Monterrey (p . 12), - , -- San-Andreas. , Jalisco-Nic.

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Publication authorized by the Director of Instituto de Geologia, Universidad Nacional Autónoma de México.     

A diverse,high-latitude ichnofauna from the Late Cretaceous Wapiti Formation,Alberta, Canada

The Wapiti Formation in west-central Alberta preserves one of the most diverse Late Cretaceous terrestrial track records yet identified in Canada. At least seven morphotypes are recognized and attributed to mammals, small reptiles or amphibians, tyrannosaurids, medium-sized theropods, hadrosaurids, and ankylosaurs. Most tracks occur isolated on slump blocks associated with latest Campanian (Wapiti Formation unit 4) exposures found along Pipestone Creek and Red Willow River. With the possible exception of hadrosaurids, tracks provide some of the most compelling evidence for the occurrence of such taxa within the Wapiti Formation ecosystem. The apparent absence of ceratopsian tracks is surprising considering their bones are abundantly preserved in nearby monodominant bonebeds. The overall faunal signal represented by the Wapiti Formation trackmakers is typical of and consistent with other coeval assemblages in similar environments. The Wapiti Formation tracks, combined with the known fossil bone record, provide another data point in a growing palaeobiogeographical picture of the dinosaur faunas of high-latitude northwestern North America during the Late Cretaceous.     

Late Precambrian OIB magmatism in the Kuznetsk Alatau,Siberia: Geochemical features of the Kulbyurstyug Formation volcanics

Basaltoids of the Vendian–Cambrian Kulbyurstyug volcanic complex in the eastern part of Kuznetsk Alatau have a high content of titanium (TiO₂ 3–4 wt %). They are relatively enriched with LILE and HFSE (Ba 360–900, Zr 160–726, Nb 66–101, ΣREE up to 225–329 ppm), and demonstrate a fractionated spectrum of REEs (La/Yb ～ 13–17), high Nb/U (44–66), and low Th/Ta and Th/Nb. These features are comparable with derivatives of OIB (Ocean Island Basalts) magmatism. The rock geochemistry suggests the possible formation of an initial mafic melt in the garnet-bearing peridotite mantle with 2–4% degree of melting and the presence of a small amount of spinel. By the age and composition, the studied volcanics are correlated with the OIB magmatism products, occurring in the adjacent Gorny Altai and also considered to be derivatives of intraplate magmatism of Riphean–Early Cambrian age. This magmatism was caused by plume activity during formation of the Paleo-Asian Ocean.     

Molar tooth structures: Formation and specificity of carbonate diagenesis in the Late Precambrian,Middle Riphean Sukhaya Tunguska Formation of the Turukhansk Uplift,Siberia

A new way of formation of the problematic Molar Tooth (MT) structures, which, along with stromatolites, could be considered as a “visiting card” of the Riphean, was examined on the example of carbonate sediments of the Riphean Sukhaya Tunguska Formation from the Turukhansk Uplift, Siberia. These structures were formed due to the consequent replacement of oozy constituent of carbonate sediments with calcitic microsparite in the course of diagenesis with substantial shift of the dynamic equilibrium toward the solution in the sediment—porous solution—microsparite system. An excess of soluble magnesium significantly hampering precipitation of crystal cores of the future calcitic microsparite could be one of the possible causes of the shift. It is suggested that magnesium mole fraction of the porous solutions was related to the early dissolution of the metastable high-Mg calcite of the silty sediment brought from the areas of active stromatolite formation. The facies occurrence of the MT-structures indicates that they occurred in descending trails of the most productive zones of carbonate platforms tapering toward the basin. The synchronism of stratigraphic trends of the MT-structures and stromatolites in the Precambrian resulted from the evolution of carbonate-productive microbe-mineral systems which were the immediate suppliers of fine-grained carbonate sediment into external zones of carbonate platforms.     

Relative sea-level history and isostatic rebound in Newfoundland, Canada

The island of Newfoundland, Canada, is situated close to the former margins of the Laurentide ice sheet. The post-glacial sea-level history is complex, dominated by the effects of an ice-marginal crustal forebulge produced by isostatic deformation of the lithosphere. Marine fossils found above present sea-level can be ¹⁴C dated, and examination of the temporal and geographical distribution of these ¹⁴C dates in combination with geomorphological indicators of past sea-levels indicates regional trends of relative sea-level change. For most of the island (apart from the Northern Peninsula) no samples have been recovered that date younger than 8000 BP. suggesting that sea-level lay below the present one in these areas for the last 8000 years. The same areas commonly show geomorphological evidence for stands of sea-level both above and below present sea-level. This evidence is interpreted as showing that over most of Newfoundland, following deglaciation, sea-level fell to below present levels, and subsequently rose to the modern level. Exceptions to this pattern are the north of the Northern Peninsula, which shows a history of continuous emergence, or a more complex pattern of sea-levels falling below present, subsequently rising above present, and currently falling; and the northeast Avalon Peninsula, which may have had sea-levels below present throughout post glacial times. This pattern of relative sea-level change is interpreted as being mostly due to isostatic recovery, with the main factor being northerly migration of the forebulge. Mapping the time at which sea-level fell below the present level allows estimation of the rate of northerly migration and collapse of the forebulge at between 4.5 and 11 km/100 years; this is considerably faster than previous estimates.     

Precambrian metamorphic conditions and crustal evolution,northeastern Alberta,Canada

A complex of Precambrian polymetamorphic gneisses and granitoids of the Churchill structural province, northeastern Alberta, Canada has been examined structurally, petrographically, chemically and geochronologically. An Archean basement gneiss complex is indicated by Rb-Sr dating of pegmatites which cut both gneisses and granitoids (2470 ± 26 Ma with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7030 ± 0.0008). A high-pressure granulite facies (M₁) mineral assemblage and older structures (D₁) are assigned to the Archean. A moderate-pressure granulite facies (M_2.1), a low-pressure amphibolite facies (M_2.2), a greenschist facies (M_2.3), and younger structures (D₂) are of Aphebian age. Formation of granitoids by anatexis of the pre-existing Archean basement complex during M_2.1 is indicated by their Aphebian ages (ca. 1900 Ma) and high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7100 ± 0.0018). The path of retrograde metamorphism is linked with relatively slow rates of uplift and cooling. Late Aphebian sediments attained low-grade greenschist facies metamorphism only and are younger than the other metamorphic rocks. The tectonic evolution of this Precambrian mobile belt during the Aphebian contrasts with the stable Archean cratonic block in the Slave province to the north.     

Late Precambrian Metamorphic Complexes of the Ulutau Massif (Central Kazakhstan): Age,Composition, and Formation Settings of Protoliths

Geotectonics - This work presents the results of a study of metamorphic rocks of the Bekturgan and Balazhezdy groups of the Precambrian Ulutau massif (Central Kazakhstan), which have been...     

Holocene carbonate sedimentation in Lake Manitoba, Canada

The carbonate mineral suite of the modern offshore bottom sediment of the South Basin of Lake Manitoba consists mainly of high magnesian calcite and dolomite with minor amounts of low-Mg calcite and aragonite. The high-Mg calcite is derived from inorganic precipitation within the water column in response to supersaturation brought about by high levels of organic productivity in the basin. Both dolomite and pure calcite are detrital in origin, derived from erosion of the surrounding carbonate-rich glacial deposits. Aragonite, present only in trace amounts in the offshore sediments, is bioclastic in origin. The upward increase in the amount of magnesian calcite in the post-glacial sediment record is attributed to increasing photosynthetic utilization of CO₂ in the lake. Stratigraphic variation in the amount of magnesium incorporated into the calcite lattice is interpreted as reflecting a variable magnesium input to the lake from ground water and surface runoff, and possibly variable calcium removal in the precipitating lake water. The effects of long-term chemical weathering at the source and size segregation explain the changes in dolomite content throughout the section.     

Geochemistry of the Late Precambrian Sturt Tillite,Flinders Ranges,South Australia

Analyses of major oxides and some trace elements (Ga, Rb, Sr, and B) were carried out on 25 samples of tillite matrix materials of the major Late Precambrian glacial episode in South Australia. The results indicate the dominantly granitic nature of the source rocks and suggest deposition under marine glacial conditions.     

Mercury in lake sediments of the Precambrian Shield near Huntsville, Ontario, Canada

 Long sediment cores (>1 m) were collected from eight Precambrian Shield lakes in southern Ontario, Canada and analyzed for mercury (Hg), loss-on-ignition (LOI), and a suite of 36 other elements. Results indicated at least 100-fold variation in sediment Hg concentrations between lakes in close proximity (from 450 ppb), comparable to the variation reported for lakes across the whole of Canada. Strong areal correlations between Hg concentrations and LOI (r ² =0.77), between Hg and other trace element concentrations (Pb, Zn, Cd, Sb, As, Br), and similarities in the vertical concentration profiles of Hg and LOI, all point to the importance of organic matter in the release, transport and redistribution of metals in watershed systems. The spatial pattern of Hg concentrations in deep, precolonial sediments (>20 cm) was found to mirror the pattern of Hg concentrations in modern surface sediments, an observation that was confirmed in a follow-up survey (r ² =0.85;n=25 lakes), indicating that natural processes govern the unequal distribution of Hg among these lakes. Between-lake differences in surface sediment Hg concentrations normalized to organic carbon (Hg/C) were also reflected by Hg concentrations in smallmouth bass normalized to 35 cm length (R ² =0.63;n=15 lakes). The latter relationship suggests that smallmouth bass and lake sediment indicators provide mutually supportive information regarding Hg loading to the lacustrine environment from geological sources in the watershed system. Received: 31 October 1996 · Accepted: 27 May 1997     

Facies, geometry and geological significance of Late Ordovician (early Caradocian) coral bioherms: Lourdes Formation, western Newfoundland

Late Ordovician coral bioherms in the Lourdes Formation of western Newfoundland exhibit a complex mixing of architectural elements, including framework, boundstone and suspension deposits. The bioherms occur within a narrow (16 m) stratigraphic interval, and a prominent unconformity truncates the interval of bioherm growth and tops of many of the bioherms. The buildups developed along a carbonate ramp. They occur isolated and in groups, individuals in groups are aligned in parallel orientation. The sizes of the bioherms range from small (50–100 cm) coral piles to columnar and dome‐shaped masses (1–15 m); however, topographic relief was never more than ≈1 m. Bioherm construction reflects: (i) stacking of the tabulate coral Labyrinthites chidlensis, and less common stromatoporoids; (ii) accumulation of microbial‐stromatoporoid boundstone and suspension deposits within shelter cavities between corals; and (iii) detrital bioherm‐flank skeletal grainstone beds. Trypanites borings are common in the tops of coral heads. The bioherms exhibit three growth‐development stages: (i) seafloor stabilization, wherein rare, abraded coral colonies lie scattered within pelmatozoan/skeletal grainstone lenses; (ii) colonization, wherein corals (L. chidlensis), rare stromatoporoids (Labechia sp.), and other biota (bryozoans) produced a bioherm overlying the basal sediment base; and (iii) diversification, which is marked by a more diverse range of fauna and flora as well as occurrence of shelter‐cavity deposits. The diversification stage usually makes up more than 70% of a bioherm structure, and, in some defines multiple periods of start‐up and shut‐down of bioherm growth. The latter is defined by bored omission surfaces and/or deposition of inter‐bioherm sediment. The Lourdes bioherms have a similar ecological structure, biotic diversity and depositional environment to patch reefs in the equivalent Carters Limestone in Tennessee. The mixture of coral stacking and boundstone as architectural elements identify an Early Palaeozoic transition of reef‐design development along shallow‐water platforms that began to displace the muddy (boundstone, bafflestone) carbonate buildups more typical of the Early and Middle Ordovician time.     

Geochemistry and tectonic setting of the late Precambrian Holyrood plutonic series of eastern Newfoundland

Major and trace element chemistry suggest that the Holyrood plutonic series is a co-magnetic calc-alkaline suite, formed at about 5 kb P_H2O by fractionation of plagioclase, amphibole and clinopyroxene from a gabbroic magma which was derived from the upper mantle. It appears unlikely that the series is genetically related to the Harbour Main volcanic rocks, either magmatically or by hybridization. Chemical comparison of the Holyrood series with suites from known tectonic environments suggest that this region approximated a ‘basin and range’ type of tectonic setting during formation of the Holyrood plutonic series.     

Modern pollen spectra from the tundra-boreal forest transition in northern Newfoundland, Canada

Percentage pollen diagrams are presented and analysed by step-wise discriminant analysis. Arboreal taxa show little variation between communities. Non-arboreal, local taxa display substantial variability, but are good indicators of community composition and structure, and provide reliable elements for the palynological characterization of communities. The discriminant analysis indicates a distinctiveness for most communities that is surprisingly high considering the small size of many of the vegetation units within the mosaic.     

Recent sedimentation events at the head of Saguenay Fjord,Canada

Unbioturbated marine sediments containing a record of high river discharge events occur at the head of Saguenay Fjord, near Saint Fulgence, eastern Canada. Preservation of allochthonous benthonic foraminifera, recognition of occasional rapid sedimentation events associated with the spring runoff of the Saguenay River, and the unmixed character of the sediment can be used in conjunction with several dating techniques to obtain a temporal resolution of paleoriverine events on a time scale of months to years. The geologic and geochemical record of the upper 150 cm of sediment reflects (1) the anoxic character of the benthic environment, resulting from the high flux of terrigeneous material to the bottom; (2) the transport and deposition of landslide-derived sediment into the head of the fjord over several years; (3) an indication of the nature and timing of dissolution processes that have altered or totally eliminated the allochthonous calcareous microfossil assemblage from the recycled sediment; and (4) a cyclic depositional pattern that may be useful in reconstructing pateoclimatologic trends that have influenced annual river discharge of this drainage system over the past millennium.     

中国晚前寒武纪微古植物研究

通过对近20年来微古植物研究成果的总结,得出如下五个结论:1)中国的晚前寒武纪发现了微古植物约128属,569种,可分为四大组合.2)长城系(14~18亿年左右)主要是以细菌和蓝藻为代表的原核细胞生物占有生物界的时期,但其中已有真核细胞生物出现.另外有Chuaria状等化石的出现和广泛分布.3)蓟县系(10~14亿年左右)是真核细胞中的高级藻类大量出现时期,红藻、褐藻,蓝藻相对减少.4)青白口系(8~10亿年左右)是褐藻植物相对繁盛时期,并有Chuaria及Shouhsienia等化石.5)震旦系下统(7~8亿年左右)生物群特征与青自口系相近似,仍以藻类植物为主,有少量后生动物.震旦系上统(6~7亿年左右)动物界和植物界都有显著变化,微古植物出现新的类型,后生植物和软躯体的后生动物大量繁衍,末期有海绵及个别软舌螺类等具骨骼的后生动物.寒武纪开始,有大量多门类小壳动物,植物界则有刺球藻亚群,这表明生物界已发展到一个新阶段.     

Late pleistocene sedimentation history of the Shirshov Ridge, Bering Sea

The analysis of the lithology, grain-size distribution, clay minerals, and geochemistry of Upper Pleistocene sediments from the submarine Shirshov Ridge (Bering Sea) showed that the main source area was the Yukon-Tanana terrane of Central Alaska. The sedimentary materials were transported by the Yukon River through Beringia up to the shelf break, where they were entrained by a strong northwestward-flowing sea current. The lithological data revealed several pulses of ice-rafted debris deposition, roughly synchronous with Heinrich events, and periods of weaker bottom-current intensity. Based on the geochemical results, we distinguished intervals of an increase in paleoproductivity and extension of the oxygen minimum zone. The results suggest that there were three stages of deposition driven by glacioeustatic sea-level fluctuations and glacial cycles in Alaska.